U.S. patent number 5,827,344 [Application Number 08/786,568] was granted by the patent office on 1998-10-27 for method of making glass.
This patent grant is currently assigned to Pilkington PLC. Invention is credited to Thomas Gordon Cochrane, Helen Louise Eaves, Kenneth Melvin Fyles.
United States Patent |
5,827,344 |
Fyles , et al. |
October 27, 1998 |
**Please see images for:
( Certificate of Correction ) ** |
Method of making glass
Abstract
A method of making glass in which a first glass composition is
fed to a furnace and the densities of such glass is determined. The
composition is then changed to produce a second glass which has
substantially different properties from the first glass, the change
to the composition being such that the desired properties are
produced in the second glass while simultaneously maintaining the
densities of the second glass substantially equal to that of the
second glass. The first glass may be a clear glass while the second
glass may be a tinted glass. In such a case, the tinted glass may
contain iron and the densities are maintained substantially equal
by utilizing the iron to replace calcium oxide in the clear glass
composition.
Inventors: |
Fyles; Kenneth Melvin
(Lancashire, GB), Eaves; Helen Louise (Cheshire,
GB), Cochrane; Thomas Gordon (Lancashire,
GB) |
Assignee: |
Pilkington PLC (St. Helens,
GB)
|
Family
ID: |
10787752 |
Appl.
No.: |
08/786,568 |
Filed: |
January 21, 1997 |
Foreign Application Priority Data
|
|
|
|
|
Jan 30, 1996 [GB] |
|
|
01780/96 |
|
Current U.S.
Class: |
65/134.1; 65/121;
65/134.3 |
Current CPC
Class: |
C03C
1/10 (20130101); C03B 5/173 (20130101) |
Current International
Class: |
C03B
5/173 (20060101); C03B 5/00 (20060101); C03C
1/00 (20060101); C03C 1/10 (20060101); C03B
005/26 (); C03B 005/16 (); C03B 005/18 (); C03B
005/28 () |
Field of
Search: |
;65/29.12,121,134.1,134.3,134.5,134.9,145 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Silverman; Stanley S.
Assistant Examiner: Ruller; Jacqueline A.
Attorney, Agent or Firm: Howrey & Simon
Claims
We claim:
1. A method for making different glasses, which comprises:
(1) supplying a glass making composition to a glass making furnace
and forming a first glass; and
(2) changing the glass making composition that is being supplied to
the glass making furnace by interchanging iron oxide and alkaline
earth metal oxide in the composition so that the density of the
glass produced after said change in glass making composition is
within 0.01 g/cm.sup.3 of the density of the glass produced before
said change in glass making composition to form a second glass.
2. A method of making glass as recited in claim 1 wherein at least
one of said first and said second glasses is a clear glass.
3. A method as recited in claim 1 wherein at least one of said
first and said second glasses is a tinted glass.
4. A method as recited in claim 1 wherein both of said glass making
compositions form tinted glass containing iron oxide.
5. A method as recited in claim 4 wherein at least one of said
tinted glasses contains at least 0.7 weight% iron.
6. A method as recited in claim 4 wherein at least one of said
tinted glasses contains at least 2 weight% iron.
7. A method as recited in claim 1 wherein one of said first and
second glasses is a clear glass soda-lime-silica composition of
SiO.sub.2, Na.sub.2 O, CaO, MgO, K.sub.2 O and Al.sub.2 O.sub.3 and
the other of said first and second glasses is a tinted glass which
includes at least Fe.sub.2 O.sub.3, CaO, SiO.sub.2, Na.sub.2 O,
MgO, K.sub.2 O and Al.sub.2 O.sub.3.
8. A method as recited in claim 7, wherein the concentration of CaO
and MgO are each higher in said clear glass than in said tinted
glass whereby the densities of the two glasses are maintained
substantially equal to one another.
9. A method as recited in claim 4 wherein both said first and
second glasses contain Fe.sub.2 O.sub.3, one of said first and said
second glasses containing more Fe.sub.2 O.sub.3 than the other of
said first and second glasses, wherein the densities of the two
glasses are maintained substantially equal by reducing the amount
of CaO in said glass containing the greater amount of Fe.sub.2
O.sub.3 relative to the amount of CaO present in said glass
containing the lesser amount of CaO.
10. A method as recited in claim 1 wherein one of said first and
said second glasses contains:
and the other of said first and said second glasses contains:
while the proviso that the amount of MgO tends to (B-X)% when the
amount of CaO tends to [(A-0.5X)%] (A-1.5X)%.
11. A method as recited in claim 10 wherein A is from 5% to 9.5%, B
is from 0% to 5%, C is from 10% to 18%, D has a maximum value of
75% with the amount of SiO.sub.2 lying within the range of 68% to
73% and the amount of Al.sub.2 O.sub.3 lying within the range of 0%
to 5%, and X lies within the range of from 0.7% to 5%.
12. A method as recited in claim 1 wherein the difference in
density between said first glass and said second glass is less than
0.005 g/cm.sup.3.
13. A method as recited in claim 1 wherein each of said glass has a
refractive index and said refractive indices differ by less than
0.004.
14. A method as recited in claim 4 wherein the iron content,
measured as Fe.sub.2 O.sub.3, of said compositions producing said
first and said second glasses differs by at least 1%.
15. In a method for changing the glass produced from a continuous
glass making process, which comprises continuously supplying a
glass making composition to a glass making furnace and forming
glass, the improvement which comprises:
changing the glass making composition, which contains iron oxide or
calcium oxide or both, by interchanging iron oxide and calcium
oxide in the composition so that the density of the glass produced
after said change in glass making composition is within 0.01
g/cm.sup.3 of the density of the glass produced before said change
in glass making composition.
16. The method according to claim 15, wherein iron oxide is
interchanged with calcium oxide and magnesium oxide so that the
density of the glass produced after said change in glass making
composition is within 0.01 g/cm.sup.3 of the density of the glass
produced before said change in glass making composition.
Description
FIELD OF THE INVENTION
The present invention relates to a method of making glass. More
particularly, the present invention relates to a method of making
glass preferably, but not essentially, by the float process which
permits the changeover time from making a clear glass to a tinted
glass and vice versa to be considerably shortened.
BACKGROUND OF THE INVENTION AND PRIOR ART DISCUSSION
It is well known to make both clear and tinted glasses by the float
process. At the present time, tinted glasses are much used in
automotive vehicles. Such tinted glasses are not provided simply
for aesthetic reasons. Clear glass does, of course, provide
excellent luminous radiation transmission but has the consequential
drawback of permitting other, unwanted radiation to enter the
interior of the vehicle. Thus solar heat radiation, in both the
visible and infra-red regions of the electromagnetic spectrum, can
cause the temperature in the interior of the vehicle to become
sufficiently high as to cause discomfort to the occupants and/or
damage to goods being transported. Moreover, clear glass allows a
high proportion of ultraviolet radiation to pass therethrough and
it is well known that such radiation causes the embrittling of
plastics materials and the fading of the colours of fabrics in the
interior of the vehicle.
To alleviate these problems, it is well known to add colorants to
the basic, clear glass composition. In particular, it is extremely
well known to employ iron oxide as the colorant Iron oxide
(Fe.sub.2 O.sub.3) is particularly beneficial because it contains
iron in both the ferric and ferrous states. Ferric iron reduces the
amount of ultraviolet radiation that is transmitted through the
glass whilst ferrous iron absorbs radiation in the near infra-red
region at about 1050 nm.
However, the use of iron oxide does have disadvantageous side
effects. In particular, it increases the densities of the glass.
The most obvious drawback of this is that the weight of the vehicle
in which the glass is incorporated is increased. From a
manufacturing point of view, particularly on a float line, a far
more serious problem manifests itself. For commercial reasons float
lines are not usually dedicated to making one particular type of
glass. For example, a float line may be used for making clear
glass, then for making a tinted glass and then restored to making
clear glass. It will be readily appreciated that the changeover
cannot be effected instantaneously.
When a changeover from clear glass to a tinted glass is made, the
tinted glass will not be of the desired quality until all of the
colorant is uniformly incorporated in, that is to say, mixed into,
the glass. It takes longer for this to be achieved if certain
colorant materials, such as iron oxide, are used. Similarly, when
the reverse changeover is made, the clear glass must be completely
clear. In other words, there must not be any streaks of colour in
the glass.
When the changeover from clear to tint is effected, the changeover
is retarded by the fact that the colorant has a higher densities
than the molten clear glass and tends to sink to the bottom of the
melter. The mixing of the colorant with the clear glass
constituents is, therefore, somewhat inefficient and takes a
considerable length of time to optimise itself. Until optimal
mixing is attained, the tinted glass will not be of an acceptable
commercial quality. When the run of making tinted glass is
completed, the colorant again tends to settle on the bottom of the
tank and is only removed slowly therefrom. These changeover times,
particularly the changeover from tinted glass to clear glass can be
very long, of the order of weeks. From a commercial point of view,
this represents a significant disadvantage.
A further problem is that of devitrification. When making a tinted
glass, particularly one containing iron oxide, there is a greater
tendency for a build-up of devitrified glass on the bottom of the
furnace at the working end to occur.
The problems of incomplete mixing and devitrification are, in
glass-making terms, problems on a macro-scale. There is also a
minor-scale problem which occurs when the composition of the glass
is changed, such as when there is a change-over in a furnace from
making one kind of glass to a second kind of glass. This is the
problem of changes occuring in the refractive index within the
glass being formed and is commonly known as "ream". This manifests
itself in the form of optical distortion when one looks through the
glass.
Still further, and alluded to above, vehicle manufacturers require
the glass which they use in their vehicles to have ever lower
weight but still to have the particular radiation transmission or
absorption properties. Accordingly, glass manufacturers are
attempting to make thinner glass having the desired properties.
According to the Lambert-Beer law, the thickness of a glass (or the
concentration of a colorant species) is linked with the visible
transmission of the glass. In essence, this states that as the
thickness of the glass is halved, the internal optical density of
the glass will also halve. Accordingly, in order to make a glass
having a thickness of 2 mm having the same radiation transmission
or absorption properties as a glass having a thickness of 4 mm, it
is usually necessary to double the concentration of the colorant.
Of course, if the concentration of the colorant is doubled, the
problems outlined above caused by the higher densities of the
colorant compared with that of the clear glass composition are
exacerbated.
OBJECTS OF THE INVENTION
The present invention therefore seeks to provide a method of making
glass in which the above-described problems are at least minimized.
In particular, the present invention seeks to provide a method of
making glass so that the changeover time when a float line is
changed from making a first type of glass to a second type of glass
is substantially reduced.
SUMMARY OF THE INVENTION
According to the present invention, there is therefore provided a
method of making glass comprising the steps of producing a first
glass in a furnace, measuring the densities of the glass thus
produced and altering the composition fed to the furnace such that
a further glass having significantly different properties from the
first glass is produced, wherein the alteration to the composition
is so selected as to produce the desired properties in the further
glass whilst simultaneously maintaining the densities of the
further glass substantially equal to that of the first glass.
We have surprisingly found that if the compositions of the
different glasses made in a particular furnace are selected so that
the densities of all of the glasses made in that furnace, measured
at 25.degree. C., are substantially the same, the changeover from
making one commercially acceptable glass to another commercially
acceptable glass can be effected much more rapidly. The term
"substantially the same densities" is defined as meaning that the
densities are within 0.01, preferably within 0.005, of one another.
Moreover, we have found that if the densities of the different
glasses are matched, the refractive indices tend also to be more
closely matched. Accordingly, we have found that, by carrying out
the method of the present invention, the problem of ream may also
be alleviated.
Preferably, the first glass is a clear glass and the further glass
is a tinted glass containing iron.
Alternatively, both said first and second glasses contain Fe.sub.2
O.sub.3 characterised in that the densities of the two glasses are
made substantially constant by reducing the CaO content in the
glass containing more Fe.sub.2 O.sub.3 relative to the glass
containing less Fe.sub.2 O.sub.3.
Glass used in vehicles and buildings is usually of the
soda-lime-silica type and the major constituents thereof are
SiO.sub.2, Na.sub.2 O, CaO, MgO, K.sub.2 O and Al.sub.2 O.sub.3. Of
these, the lightest component is SiO.sub.2 which, when fused, has a
densities of approximately 2.2. Most glass manufacturers have a
basic clear glass composition which they maintain substantially
consistent. If they then wish to make a tinted glass containing
iron, this is effected in one of two ways. Firstly the composition
may be modified by selecting the appropriate amount of iron oxide
to be added (in weight %) and reducing the amount of SiO.sub.2
present in the composition by the same amount. Alternatively, the
iron oxide may simply be added to the other constituents of the
clear glass composition. It will be readily apparent that, if the
amounts are calculated in weight %, this latter procedure has the
effect of slightly reducing the weight percentage of all of the
components originally present
We have found that each of the constituents of a glass making
mixture have an effect on the densities of the glass which is
produced. Whilst this may appear, at first sight, to be
self-evident, we have surprisingly found that the effects produced
are not predictable. For example, the densities of iron oxide, in
the form of Fe.sub.2 O.sub.3, and CaO are approximately 5.2 and 3.2
respectively. However, for each weight percent of Fe.sub.2 O.sub.3
used to replace one weight percent of SiO.sub.2, the densities of
the glass rises by approximately 0.0150. For each weight percent of
CaO used to replace one weight percent of SiO.sub.2, the densities
rises by 0.0149. This is totally unexpected on the basis of the
densities of the Fe.sub.2 O.sub.3 and the CaO. Similarly, from
their densities, one would expect K.sub.2 O to have a greater
effect on the density of the glass than Na.sub.2 O. However, again
referring to the replacement of one weight percent of SiO.sub.2 by
one weight percent of each of these alkali metal oxides, we have
found that the sodium oxide increases the densities of the glass by
0.0078 whilst the potassium oxide only increases it by 0.0056.
From the above, it will be readily apparent that if the tinted
glass is to contain Fe.sub.2 O.sub.3 in relatively large
amounts--say from 0.7 to 5 weight %--the densities of the glass
would be substantially increased if the usual procedure of reducing
the amount of SiO.sub.2 in an amount corresponding to that of the
iron oxide added were adopted. However, it will be equally apparent
from the above discussion that if the amount of CaO is reduced by
an amount corresponding to the amount of Fe.sub.2 O.sub.3 added,
the effect on the densities will be very small (an increase of
approximately 0.0001 per weight percent of Fe.sub.2 O.sub.3
added).
However, particularly if there is a large amount of iron in the
tinted glass, a straight exchange of Fe.sub.2 O.sub.3 for CaO can
give rise to problems. In particular, although lowering the amount
of CaO lessens the chance of devitrification due to wollastonite
(calcium silicate) occurring, too low an amount of calcium present
tends to encourage the formation of phases such as diopside or
silica-rich primary phases such as tridymite. Both of these are
harder to remove than wollastonite, particularly the silica-rich
phases.
Accordingly, it may be preferred if the MgO content is
simultaneously reduced along with the CaO. The removal of calcium
oxide and/or magnesium oxide can lead to a change in the working
temperature (also known as the log4 viscosity because this is the
temperature at which the glass has a viscosity of 10.sup.4 poise).
Since a change in the working temperature is not usually regarded
as desirable by glass manufacturers because it may necessitate
physical changes to other parameters it may therefore be desirable
if this is counterbalanced by a slight increase in the amount of
Na.sub.2 O and K.sub.2 O in the composition.
In a particularly preferred embodiment of the present invention,
the first glass contains A% CaO, B% MgO, C% Na.sub.2 O plus K.sub.2
O and D% SiO.sub.2 plus Al.sub.2 O.sub.3, and the second glass
contains X% total iron (expressed as Fe.sub.2 O.sub.3), (A-0.5X)%
to (A-1.5X)% CaO, B% to (B-X)% MgO with the proviso that the amount
of MgO tends to (B-X) when the change in CaO is least, C to
(C+0.5X) Na.sub.2 O plus K.sub.2 O and D% SiO.sub.2 plus Al.sub.2
O.sub.3 with sufficient changes to cause the total contents to be
100 weight %.
As previously mentioned, the tinted glasses are intended, in most
cases to be so-called "high performance glasses", that is to say,
they have low infra-red and ultraviolet radiation transmittance. In
a particularly preferred embodiment of the present invention, the
glasses are primarily intended for use as either privacy glazing or
as the glazing for a sunroof in a vehicle. To produce such glazing,
the iron content in the composition needs to be relatively high and
the method of the present invention is particularly useful in
preparing glass wherein the iron oxide content is in excess of 0.7
weight percent and may be as high as 5 weight percent.
Other colorants may be used in association with the iron oxide.
Examples of such colorants are selenium, nickel oxide and cobalt
oxide. Even though these have relatively high molecular weights,
the amounts which are used are relatively small, of the order of
500 ppm or less and such small amounts have such a small effect on
the densities of the finished glass that, for the practical
purposes of the present invention, they can be ignored.
If the amount of calcium oxide is reduced as the amount of iron
oxide is increased, the working temperature of the glass remains
substantially the same. However, the liquidus temperature, that is
to say, the temperature at which the glass will begin to
crystallise under equilibrium conditions, will drop. This is
because magnesium calcium silicate (diopside) is then formed as the
primary or highest temperature phase as the amount of calcium in
the glass is reduced. This aspect of the present invention
therefore helps to prevent a build-up of devitrified glass.
Devitrification is a common problem in glasses containing high
amounts of iron oxide. The working range, which is the difference
between the working temperature and the liquidus temperature, is
thereby increased. This latter is of importance because it means
that it is easier to form the glass without crystallisation
occurring and the amount of devitrification is reduced or even
eliminated completely.
In another aspect of the present invention, there is provided a
high soda-lime-silica glass for the production of vehicle windows
having a low Direct Solar Heat Transmission by virtue of the
presence of colorants including the iron, characterised in that the
composition contains a reduced proportion of alkaline earth metal
oxides. In a preferred embodiment, the glass contains more than 2.0
weight % iron calculated as Fe.sub.2 O.sub.3 and less than 12
weight % alkaline earth metal oxides. Advantageously, the alkaline
earth metal oxide content is below 11% and, desirably, the iron
content is less than 2.5 weight %, calculated as Fe.sub.2 O.sub.3.
Glasses of this type preferably have a working range of at least
9C.
Although high iron content glasses have been made hitherto, such
glasses have either not had the desired optical properties or have
caused production difficulties of the types detailed hereinbefore.
We have surprisingly found that, by reducing the amount of alkaline
earth metal oxides present in high iron glasses to below, for
example 12%, the production difficulties are overcome whilst the
optical properties are attained.
DESCRIPTION OF PREFERRED EMBODIMENTS
The invention will be further described, by way of example only,
with reference to the following non-limitative Examples appearing
in the following Tables. In the tables:
The ferrous state is the amount of FeO (expressed as Fe.sub.2
O.sub.3), divided by the total iron oxide (expressed as Fe.sub.2
O.sub.3).
Illuminant A transmission represents the power distribution of
tungsten filament according to the 1931 Observer set.
DSHT (Direct Solar Heat Transmission) refers to solar heat
transmission integrated over the wavelength range 350 to 2100 nm
according to the relative solar spectral distribution Parry Moon
for air mass 2 direct, as detailed in ISO 9050.
UVT (ISO) for the measurement of ultraviolet radiation over the
wavelength range 280-380 nm (air mass 2 global) is from standard
ISO 9050.
UVT (PM) is the measurement of ultraviolet radiation over the
wavelength range 300 to 400 nm derived from the factors published
by Parry Moon in the Journal of the Franklin Institute 230 pp
583-617, 1940.
a* and b* are colour co-ordinates derived using the CieLAB
co-ordinate system.
The log 4 viscosity temperature is the temperature in degrees
Celsius at which the glass has a viscosity of 10,000 poise.
The liquidus temperature is determined by placing glass grains in a
gradient furnace for 16 hours then measuring the hottest
temperature at which crystal growth occurs.
Density is the mass per unit volume in grams per cubic centimeter
at 25.degree. C. measured using the Archimedes method.
W=Wollastonite
Di=Diopside
De=Devitrite
Si=Silica
Nd=Refractive Index
TABLE 1
__________________________________________________________________________
Example 1 2a 2b 3 4 5 6 7
__________________________________________________________________________
SiO.sub.2 72.7 71.77 71.4 72.7 72.7 72.2 72.7 72.7 Al.sub.2 O.sub.3
1.0 0.987 1.0 1.0 1.0 1.0 1.0 1.0 Na.sub.2 O 13.0 12.833 13.0 13.0
13.0 13.5 13.0 13.0 K.sub.2 O 0.6 0.592 0.6 0.6 0.6 0.6 0.6 0.6 MgO
4.0 3.949 4.0 4.0 3.8 3.8 3.4 2.8 CaO 8.4 8.292 8.4 7.2 7.4 7.4 7.8
8.4 SO.sub.3 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Fe.sub.2 O.sub.3 0.1
1.3 1.3 1.3 1.3 1.3 1.3 1.3 Ferrous state 20% 22% 22% III. A Trans
DSHT UVT (ISO) UVT (PM) a* b* dom .lambda. nm Colour Purity % log4
visc. 1037 (1033) (1028) 1037 1038 1030 1034 1032 temp. .degree.C.
Liquidus 1000 W 1000 W 982 Di 982 W 980 W 990 W 998 W Temp.
(T.sub.l) 998 Di 964 De 976 Di 963 De T.sub.w - T.sub.l +36.degree.
C. +33.degree. C. +28.degree. C. +55.degree. C. +56.degree. C.
+50.degree. C. +44.degree. C. +34.degree. C. Densities 2.4910
2.5086 2.5103 2.4925 2.4941 2.4987 2.4963 2.4996 Refractive 1.5180
1.5224 1.5230 1.5188 1.5188 1.5194 1.5197 1.5207 Index (Nd)
__________________________________________________________________________
Example 8 9 10 11 12 13 14 15
__________________________________________________________________________
SiO.sub.2 71.14 72.7 72.7 72.2 72.4 72.7 72.7 72.7 Al.sub.2 O.sub.3
0.98 1.0 1.0 1.5 1.5 1.0 1.0 1.0 Na.sub.2 O 12.72 13.0 13.0 14.1
14.2 13.0 13.0 13.0 K.sub.2 O 0.587 0.6 0.6 0.6 1.0 0.6 0.6 0.6 MgO
3.91 3.4 3.4 4.0 1.0 3.6 3.0 0 CaO 8.22 6.8 6.8 5.1 7.4 7.1 5.4 8.4
SO.sub.3 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Fe.sub.2 O.sub.3 2.2 2.2
2.2 2.2 2.2 1.7 4.0 4.0 Ferrous state 22% 22% 30% 22% 33% 33% 22.4%
21% Co.sub.3 O.sub.4 295 275 235 285 235 90 500 500 Se 15 16 17 24
18 10 20 13 NiO 250 250 75 150 0 50 400 400 III. A Trans 28.1 31.5
32.0 28.5 34.1 51.5 11.0 16.0 DSHT 20.9 24.1 21.4 21.1 22 32.5 9.0
14.4 UVT (ISO) 4.9 6.6 6.1 6.1 8.7 14.4 0.5 0.8 UVT (PM) 15.4 19
17.6 17.4 22.6 32 3.4 5.6 a* -7.0 -6.4 -6.3 -5.8 -7.1 -7.6 -7.7
-8.9 b* -0.6 -1.5 -0.4 -1.7 -6.4 -0.5 +2.2 -2.8 dom .lambda. nm
493.7 492 494 491 486 494 507 491 Colour Purity % 5.7 6 4.8 6.1
11.4 4.2 4.5 11.1 Log 4 visc. (1027) 1042 1042 1038 1012 (1040)
1044 temp .degree. C. Liquidus 1016 Di 970 970 990 Di 958 De 972
980 Si Temp. (T.sub.l) W/Di W/Di W/Di T.sub.w - T.sub.l +11.degree.
C. +72.degree. C. +72.degree. C. +48.degree. C. +54.degree. C.
+68.degree. C. +64.degree. C. Density 2.5189 2.4951 2.4965 2.4884
2.4995 2.4944 2.4983 2.5153 Refractive Index 1.5253 1.5197 1.5197
1.5202 1.5194 1.5216 1.5259
__________________________________________________________________________
Example 16 17 18 19 20 21 22
__________________________________________________________________________
SiO.sub.2 72.0 72.7 72.7 72.7 72.7 72.7 72.7 Al.sub.2 O.sub.3 1.9
1.0 1.0 1.0 1.0 1.0 1.0 Na.sub.2 O 15.0 13.0 13.0 13.0 13.0 13.0
13.0 K.sub.2 O 0.6 0.6 0.6 0.6 0.6 0.6 0.6 MgO 0 4.0 3.45 3.8 3.7
3.6 3.7 CaO 6.2 4.4 6.8 7.5 7.4 7.1 7.4 SO.sub.3 0.2 0.2 0.2 0.2
0.2 0.2 0.2 Fe.sub.2 O.sub.3 4.0 4.0 2.15 1.1 1.3 1.7 1.3 Ferrous
state 20.5% 21% 26% 27% 23% 34% 27% Co.sub.3 O.sub.4 500 500 200
113 130 170 130 Se 43 12 26 19 15 21 10
NiO 400 400 75 50 50 75 50 III. A Trans 9.3 16.7 32.5 52 52.2 38.9
53.4 DSHT 8.8 15.1 23.4 43 43 26 41.5 UVT (ISO) 0.5 0.6 5.4 18 16
11 18.4 UVT (PM) 3.2 4.6 16 36.2 34.6 24.1 37.7 a* -2.8 -10.0 -3.9
-1.6 -3.2 -5.5 b* 5.9 -0.2 +4.9 +3.2 +0.8 +0.9 dom .lambda. nm 568
495.8 561 586 498 498 490 Colour Purity % 10.7 8.4 5.1 2.7 1.5 3
4.2 log4 visc. 1005 temp. .degree.C. Liquidus 955 De Temp.
(T.sub.l) 950 Si T.sub.w - T.sub.l +50.degree. C. Densities 2.5074
2.4899 2.4933 2.4938 2.4941 2.4947 2.4944 Refractive Index 1.5214
1.5202
__________________________________________________________________________
Example 23 24 25 26 27 28
__________________________________________________________________________
SiO.sub.2 72.7 72.7 72.7 72.7 72.7 72.7 Al.sub.2 O.sub.3 1.0 1.0
1.0 1.0 1.0 1.0 Na.sub.2 O 13.0 13.0 13.0 13.0 13.0 13.0 K.sub.2 O
0.6 0.6 0.6 0.6 0.6 0.6 MgO 3.6 3.7 3.8 3.6 3.6 3.4 CaO 7.1 7.4 7.5
7.1 7.1 6.8 SO.sub.3 0.2 0.2 0.2 0.2 0.2 0.2 Fe.sub.2 O.sub.3 1.7
1.3 1.1 1.7 1.7 2.2 Ferrous state 27% 27% 28% 36.5% 37.5% 28.4%
Co.sub.3 O.sub.4 10 45 13 170 170 255 Se 56 26 31 10 5 12 NiO 75 50
50 75 75 150 III. A Trans 35 53 56 43.3 44.7 32.7 DSHT 27 39 43 28
28.6 23 UVT (ISO) 5.3 13.3 15 13.9 15.4 7 UVT (PM) 12 29.5 31.5 31
33.4 19.6 a* +8.0 -1.0 +1.4 -7.9 -8.7 -7.7 b* +26.9 +10.0 +13.4
-5.4 -7.3 -4.0 dom .lambda. nm 582 575 578 488 487 489 Colour
Purity % 38.6 11 16 10.0 12.1 9.3 log4 visc. temp. .degree.C.
Liquidus 976 W Temp. (T.sub.l) 970 Di T.sub.w - T.sub.l Densities
2.4940 2.4949 2.4944 2.4961 2.4955 2.4967 Refractive index
__________________________________________________________________________
Example 29 30 31 32
__________________________________________________________________________
SiO.sub.2 72.6 72.6 70.6 70.6 Al.sub.2 O.sub.3 0.1 0.1 0.91 0.91
Na.sub.2 O 13.9 13.9 13.7 13.7 K.sub.2 O 0.03 0.03 0.57 0.57 MgO
4.1 3.5 4.0 3.4 CaO 8.9 7.3 9.76 8.16 SO.sub.3 0.23 0.23 0.27 0.27
Fe.sub.2 O.sub.3 0.11 2.2 0.1 2.2 Ferrous state 20% 24% 20% 24%
Co.sub.3 O.sub.4 275 275 Se 23 22 NiO 250 250 III. A Trans 29.4 29
DSHT 23.5 23.1 UVT (ISO) 5.4 4.5 UVT (PM) 16.4 14.6 a* -5.1 -5.4 b*
+1.4 +2.7 dom .lambda. nm 503 522.2 Colour Purity % 2.4 2.1 log4
visc. 1014 1020 1000 1010 temp. .degree.C. Liquidus 1008 W 996 Si
1028 W 990 W Temp. (T.sub.l) 988 W T.sub.w - T.sub.l +6 +24 -28 +20
Densities 2.5017 2.5017 2.5176 2.5237 Refractive index 1.5201
1.5221 1.5249 1.5268
__________________________________________________________________________
TABLE 2
__________________________________________________________________________
Example 1 8 9 10 11 12 13 14
__________________________________________________________________________
SiO.sub.2 72.7 71.14 72.7 72.7 72.7 72.4 72.7 72.7 Al.sub.2 O.sub.3
1.0 0.98 1.0 1.0 1.5 1.5 1.0 1.0 Na.sub.2 O 13.0 12.72 13.0 13.0
14.1 14.2 13.0 13.0 K.sub.2 O 0.6 0.587 0.6 0.6 0.6 1.0 0.6 0.6 MgO
4.0 3.91 3.4 3.4 4.0 1.0 3.6 3.0 CaO 8.4 8.22 6.8 6.8 5.1 7.4 7.1
5.4 SO.sub.3 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Fe.sub.2 O.sub.3 0.1
2.2 2.2 2.2 2.2 2.2 1.7 4.0 Ferrous state 20% 22% 22% 30% 22% 33%
33% 22.4% Co.sub.3 O.sub.4 295 275 235 285 235 90 500 Se 15 16 17
24 18 10 20 NiO 250 250 75 150 0 50 400 III. A Trans 8.7 10.7 11.2
9 12.9 29.2 1.4 DSHT 5.6 7.1 6.3 5.8 7.2 14.9 1.1 UVT (ISO) 0.7 1.1
1.0 0.9 1.9 4.6 0 UVT (PM) 3.9 5.5 4.9 4.8 7.8 14.7 0.3 a* -9.1
-8.7 -8.6 -7.5 -9.4 -12.1 -7.3 b* -0.6 -1.9 -0.4 -2.1 -9.1 -0.6
+2.4 dom .lambda. nm 494.9 492.3 495.2 491.4 486 495.1 510.7 Colour
Purity % 10.1 11.0 8.6 10.9 20.8 8.9 8.2 Log 4 visc. 1037 1042
1.038 1012 1044 temp .degree.C. Liquidus 1000 W 1016 Di 970 W/Di
990 Di 958 De 972 W/Di 980 Si Temp. (T.sub.l) T.sub.w - T.sub.l
+36.degree. C. +48.degree. C. +54.degree. C. Densities 2.4910
2.5189 2.4951 2.4965 2.4884 2.4995 2.4944 2.4983 Refractive Index
1.5180
__________________________________________________________________________
Example 15 16 17 18 19 20 21
__________________________________________________________________________
SiO.sub.2 72.7 72.0 72.7 72.7 72.7 72.7 72.7 Al.sub.2 O.sub.3 1.0
1.9 1.0 1.0 1.0 1.0 1.0 Na.sub.2 O 13.0 15.0 13.0 13.0 13.0 13.0
13.0 K.sub.2 O 0.6 0.6 0.6 0.6 0.6 0.6 0.6 MgO 0 0 4.0 3.45 3.8 3.7
3.6 CaO 8.4 6.2 4.4 6.8 7.5 7.4 7.1 SO.sub.3 0.2 0.2 0.2 0.2 0.2
0.2 0.2 Fe.sub.2 O.sub.3 4.0 4.0 4.0 2.15 1.1 1.3 1.7 Ferrous state
21% 20.3% 21% 26% 27% 23% 34% Co.sub.3 O.sub.4 500 500 500 200 113
130 170 Se 13 43 12 26 19 15 21 NiO 400 400 400 75 50 50 75 III. A
Trans 2.9 1.0 2.7 11.6 29.9 29.9 16.6 DSHT 2.7 1.1 2.5 7.0 21.6
21.4 9.2 UVT (ISO) 0 0 0 0.8 6.7 5.7 2.6 UVT (PM) 0.6 0.2 0.4 4.1
18 17 8.7 a* -9.5 -2.5 -10.8 -5.5 -2.6 -5.3 -8.1 b* -3.2 5.1 0 +6.9
+5.3 +1.2 +1.4 dom .lambda. nm 491 568 496.8 561.4 568 501.2 500.9
Colour Purity % 20.2 22.5 15.4 10.9 6.2 2.7 5.1 log4 visc. 1005
temp. .degree.C. Liquidus 955 De Temp. (T.sub.l) 950 Si T.sub.w -
T.sub.l +50.degree. C. Densities 2.5153 2.5074 2.4899 2.4933 2.4938
2.4941 2.4947 Refractive Index
__________________________________________________________________________
Example 22 23 24 25 26 27 28
__________________________________________________________________________
SiO.sub.2 72.7 72.7 72.7 72.7 72.7 72.7 72.7 Al.sub.2 O.sub.3 1.0
1.0 1.0 1.0 1.0 1.0 1.0 Na.sub.2 O 13.0 13.0 13.0 13.0 13.0 13.0
13.0 K.sub.2 O 0.6 0.6 0.6 0.6 0.6 0.6 0.6 MgO 3.7 3.6 3.7 3.8 3.6
3.6 3.4 CaO 7.4 7.1 7.4 7.5 7.1 7.1 6.8 SO.sub.3 0.2 0.2 0.2 0.2
0.2 0.2 0.2 Fe.sub.2 O.sub.3 1.3 1.7 1.3 1.1 1.7 1.7 2.2 Ferrous
state 27% 27% 27% 28% 36.5% 37.5% 28.4% Co.sub.3 O.sub.4 130 10 45
13 170 170 255 Se 10 56 26 31 10 5 12 NiO 50 75 50 50 75 75 150
III. A Trans 31.2 13.7 31.3 34.2 20.8 22.3 11.9 DSHT 20.6 8.9 18.8
21.6 11.4 12.2 7.1 UVT (ISO) 7.1 0.5 4.3 4.9 4.3 5.1 1.2 UVT (PM)
19.7 2.1 13 13.8 13.8 15.8 6.1 a* -7.2 +13.3 -1.2 +3.2 -11.6 -12.5
-10.3 b* -2.5 +35.7 +15.9 +21.9 -8.2 -11.4 -5.4 dom .lambda. nm
490.4 584.1 575 578.8 487.5 486.3 489 Colour Purity % 7.5 67.1 21.8
30.7 18.3 22.1 16.9 log4 visc. 976 W temp. .degree.C. 970 Di
Liquidus Temp. (T.sub.l) T.sub.w - T.sub.l 2.4961 2.4955 2.4967
Densities 2.4944 2.4940 2.4949 2.4944 Refractive Index
__________________________________________________________________________
Example 29 30 31 32
__________________________________________________________________________
SiO.sub.2 72.6 72.6 70.6 70.6 Al.sub.2 O.sub.3 0.1 0.1 0.91 0.91
Na.sub.2 O 13.9 13.9 13.7 13.7 K.sub.2 O 0.03 0.03 0.57 0.57 MgO
4.1 3.5 4.0 3.4 CaO 8.9 7.3 9.76 8.16 SO.sub.3 0.23 0.23 0.27 0.27
Fe.sub.2 O.sub.3 0.11 2.2 0.1 2.2 Ferrous state 20% 24% 20% 24%
Co.sub.3 O.sub.4 275 275 Se 23 22 NiO 250 250 III. A Trans 9.5 9.3
DSHT 6.8 6.5 UVT (ISO) 0.8 0.6 UVT (PM) 4.4 3.6 a* -6.9 -7.2 b*
+2.1 +3.8
dom .lambda. nm 507.7 530 Colour Purity % 4.2 5 log4 visc. 1014
1020 1000 1010 temp. .degree.C. Liquidus 1008 W 996 Si 1028 W 990 W
Temp. (T.sub.l) 988 W T.sub.w - T.sub.l +6 -28 +20 Densities 2.5017
2.5017 2.5176 2.5237 Refractive Index 1.5201 1.5249
__________________________________________________________________________
In Table 1, there are shown the compositions and spectral
properties of a variety of glasses in a 2 mm thickness. In Table 2,
the spectral properties of the glasses having the compositions
shown in Table 1 are given, but at a thickness of 4 mm.
In Table 1, Example 1 is an example of a clear float glass
containing an amount of iron oxide at an impurity level. Examples
2a and 2b are glasses containing 1.2 weight percent Fe.sub.2
O.sub.3 added to the basic composition of Example 1. In Example 2a,
in accordance with one of the known techniques described
hereinbefore, the total weight percentage of the composition is now
notionally 101.2 and this must obviously be re-calculated to bring
the total back to 100%. Example 2b shows a similar composition to
Example 2a but, in this case, the extra 1.2 weight percent Fe.sub.2
O.sub.3 has been added at the expense of SiO.sub.2. All of the
other Examples up to and including Example 28 with the exceptions
of Example 8 (similar to Example 2a), Example 15 (in which the iron
oxide has been added at the expense of MgO rather than CaO) and
Example 16 (in which all of the MgO and some CaO has been removed
and has been replaced by the iron oxide) are compositions for use
in the present invention in which the densities of the iron oxide
containing glass has been balanced with the densities of the clear
glass shown in Example 1. Examples 9 to 11 and 13 to 17, in both
Tables, are green grey glasses; Examples 18 to 22 are grey glasses;
Examples 23 to 25 are bronze glasses and Examples 12 and 26 to 28
are blue glasses. As mentioned hereinbefore, there is no "standard"
clear glass composition because, for example, the various raw
materials used for making glass have varying compositions depending
upon the source from which they are obtained or the glass
manufacturer has a particular composition which he prefers to use.
Accordingly, Examples 29 and 31 show clear glasses having different
compositions from that shown in Example 1 and Examples 30 and 32
show tinted glasses, which are grey-green, having densities matched
to those of these two clear glasses respectively.
From the Tables, it will be clearly seen that the densities of the
tinted glasses are closely matched with the corresponding clear
glass. Moreover, the working range, that is to say, the difference
the working temperature and the liquidus temperature has been
increased. We have found that, by carrying out the method of the
present invention, the changeover from making a clear glass to a
tinted glass can be shortened by hours and the changeover from
tinted glass to clear glass can be shortened by days. Furthermore,
from the spectral values given, it can clearly be seen that glasses
having the requisite luminous, infra-red and ultraviolet
transmissions can be obtained.
Various modifications may be made to the method of the present
invention without departing from the scope thereof Thus, for
example, although the above description is primarily concerned with
effecting a changeover from clear glass to tinted glass and vice
versa, the method may equally easily be used for effecting a
changeover between two different tinted glasses.
* * * * *